Take the innocuous-sounding and innocent-looking gympie-gympie (Dendrocnide moroides), of the nettle family Urticaceae, for instance. This green, leafy bush with heart-shaped foliage, found commonly in rainforested areas in north-eastern Australia, the Moluccas and Indonesia, is covered with hollow, hair-like, stinging needles that contain a powerful neurotoxin that causes excruciating pain. The extreme itching is so painful that it has been known to kill dogs, horses, and drive humans mad with agony.

Plant Secrets/Video screen capturePlant Secrets/Video screen capture

The gympie-gympie's active compound, moroidin, is so persistent that it has been known to torture its victims for over a year if its stinging hairs are not removed from the skin. Even dry specimens, preserved for many decades, can still retain their powerful sting. Here's how virologist Dr. Mike Leahy explains on Oddity Central the gympie-gympie's deadly effects:

The first thing you’ll feel is a really intense burning sensation and this grows over the next half hour, becoming more and more painful. Shortly after this, your joints may ache, and you might get swelling under your armpits, which can be almost as painful as the original sting. In severe cases, this can lead to shock, and even death.

Plant Secrets/Video screen capture

Stories abound of the gympie-gympie's notorious side effects. Stung horses that have been known to die within hours, even jumping off cliffs to escape their suffering. One man was purported to have shot himself to end his pain after having foolishly used the leaf as toilet paper. Even breathing in any floating hairs can cause sneezing, rashes and nosebleeds. Entomologist and ecologist Marina Hurley, who studies various species of Australian stinging trees, has likened the gympie-gympie's effect to "being burnt with hot acid and electrocuted at the same time." Yet, there are some marsupial species, insects and birds that consume the plant's leaves and fruits with no problem. Hurley shows us the plant in this excerpt from the French documentary 'Plant Secrets':

So what is the remedy for a gympie-gympie sting? According to Wikipedia, the most effective treatment out there is pretty simple: an application of diluted hydrochloric acid to the exposed skin, and pulling the tiny stinging hairs with a wax hair removal strip -- otherwise, leaving any hairs behind will mean that the toxins will continue to be released. The gympie-gympie plant is a clear example that shows even the most innocent-looking thing in nature can pack a powerful punch, and that underestimating nature too can be a dangerous idea. More over at Wikipedia and Oddity Central.